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    <title>chaintest</title>
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    <center>Scilab Function</center>
    <div align="right">Last update : April 1993</div>
    <p>
      <b>chaintest</b> -  a three-species food chain model</p>
    <h3>
      <font color="blue">Calling Sequence</font>
    </h3>
    <dl>
      <dd>
        <tt>chaintest([f_l,b1,odem,xdim,npts])  </tt>
      </dd>
      <dd>
        <tt>[xdot]=chain(t,x)  </tt>
      </dd>
      <dd>
        <tt>[z1]=ch_f1(u)  </tt>
      </dd>
      <dd>
        <tt>[z2]=ch_f2(u)  </tt>
      </dd>
    </dl>
    <h3>
      <font color="blue">Parameters</font>
    </h3>
    <ul>
      <li>
        <tt>
          <b>f_l</b>
        </tt>: the name of the macro which code the three-species food chain model (default value <tt>
          <b> chain</b>
        </tt>).</li>
      <li>
        <tt>
          <b>odem,xdim,npts</b>
        </tt>: are optional arguments. Their meaning and syntax can be found in the <tt>
          <b>portr3d</b>
        </tt>  help</li>
    </ul>
    <h3>
      <font color="blue">Description</font>
    </h3>
    <p>
    A call to the function <tt>
        <b>chaintest()</b>
      </tt> will interactively 
    display a phase portrait of  a three-species food chain model given by:</p>
    <pre>

 ff1= f1(x(1))
 ff2= f2(x(2))

 xdot1= x(1)*(1-x(1)) - ff1*x(2)
 xdot2= ff1*x(2) -  ff2*x(3) - 0.4*x(2)
 xdot3= ff2*x(3) - 0.01*x(3)
   
    </pre>
    <p>
    and</p>
    <pre>

 f1(u)=5*u/(1+b1*u)
 f2(u)z2=0.1*u/(1+2*u)
   
    </pre>
    <p>
    The default value for <tt>
        <b>b1</b>
      </tt> is 3.0.</p>
    <p>
    The Scilab macros <tt>
        <b>chain(t,x)</b>
      </tt>,<tt>
        <b>f1(u),f2(u)</b>
      </tt> code the dynamical system</p>
    <h3>
      <font color="blue">See Also</font>
    </h3>
    <p>
      <a href="portr3d.htm">
        <tt>
          <b>portr3d</b>
        </tt>
      </a>,&nbsp;&nbsp;<a href="../nonlinear/ode.htm">
        <tt>
          <b>ode</b>
        </tt>
      </a>,&nbsp;&nbsp;</p>
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